Dentists are the health professionals most susceptible to musculoskeletal disorders, due mainly to static and awkward postures they adopt when performing dental procedures. This study aimed to analyze dentist's head, neck and trunk posture, during work while sitting on an ergonomic seat. The postures adopted by twelve dentists when sitting on an ergonomic seat, were registered using Xsens (R) MVN BIOMECH and analyzed using Visual 3D (TM) Educational Version (C-Motion, Inc. 2017) software. The percentage of time each dentist remained in a determined position was evaluated according to established limits by international standards for each type of movement. Results indicated that dentists worked with a moderate forward head position and lateral flexion is maintained most of the time in a posture which is not recommended. The trunk flexion varied between an acceptable and moderate posture, however, its lateral flexion was maintained in an acceptable posture. Neck flexion during the tasks remained acceptable, however, its lateral flexion remained in a position not recommended. This study suggests that even with the use of an ergonomic seat there is a moderate flexion and excessive lateral flexion of the head. The effect of an ergonomic seat translates into an improvement in anterior flexion of the neck. On the other hand, this device minimizes anterior flexion of the trunk and maintains lateral flexion in a neutral posture.